By Jon Keller

BOSTON (CBS) – First, let’s stipulate – the Green Line extension is a good idea, public transportation doing what it does best: going where the people are to ease traffic and pollution and unlock economic growth. And it’s too bad we don’t have unlimited funds available to build it.

But we don’t.

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And now that botched Green Line planning has brought the project to a halt with obscene cost-overruns, there’s a real risk the doubts about building it could overwhelm the benefits.

What are the risks?

From Transportation Secretary Stephanie Pollack: “…that we don’t have enough revenue to pay for the entire project, that we don’t have the management capacity, and … the risk of diverting the attention of the MBTA from its first priority.”

The Big Dig’s greatest hits, all remastered and reissued in a special commemorative edition, just in time for Father’s Day!

People close to the new plan approved by the MassDOT board Monday insist it’s a big step forward, but I lived through the Big Dig and I’m skeptical.

The feds could still look over the new fingers-crossed budget and say hey, we’re cutting our losses and pulling out. The board is demanding the state use a management method that commits the builder to a maximum cost; who are they going to get to take that multi-million-dollar risk?

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Maybe Bechtel?

One of the board members told the Globe: “We are not going to be the board that will deny the project,” a remark that does not reek of confidence.

The Green Line extension would be a sweet ride.

So would that Lexus we’ve had our eye on. But we walk away when we see the price tag on it.

And no one’s promising that won’t happen here.

Listen to Jon’s commentary:

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Jon Keller